Valve Upgrading

[bszopi]

Decided to bring up a topic which has been discussed before, and one Colin and I were talking about the other night. And that would be increasing the valve size of the Gen 3 heads. Production 3400 heads are 1.76" intake and 1.42" (IIRC) exhaust. On the previous forum, Smilinguy99 has a website that discussed upping the intake size, and proved that a 1.84" valve would physically fit into the combustion chamber. He didn't test any further interference issues though (at least, last I had heard).

Colin and I started to discuss this the other night and he mentioned increasing exhaust size instead of intake size. This began a discussion into the benefits (and also requirements) for getting more air into the CCs. Anyway, I did some quick calculations and came up with an increase to 1.80" intake and 1.45" exhaust would maintain the stock percentage between the intake and exhaust openings.

With that said, anyone care to discuss any of this further? I know I have 2 sets of heads sitting around begging to get worked on. I do want to look into upgrading the valves to a larger size, and I know there are at least a few others out there also interested.

[SappySE107]

What size valve seats can you fit in there?

[Guest]

I was trying a few different valves recently and taking some measurements.

In short this is what I have found:

A 1.76" intake valve is the largest that can be installed in the head, without major rework of the head. The valve seat on the outside is only 1.8", so leaving at least .020" around the valve for blending and strength, that leads us right to the stock 1.76" valve.
For the exhaust a 1.5" valve could be installed, but will require regrinding of the valve seat. But this leads to other problems since the valve seat would now be thinner, and may experiance dropping out of the seats, due to less area to disipate the heat.
Sp what about installing larger seats? Well there's an issue with that, the seats are already very close, and to grind the head out for a larger seat could prove to be difficult and cause problems in that already too thin area between the seats.
Another issue that arises, is because the valves are splayed, they could in theory come in contact with one another. With stock valves I believe this measurement was about .400" valve lift. With larger valves, the amount of lift will become smaller before contact is made. Now I know this should never happen in the real world, but is something to keep in mind.

[1QUICKHATCH]

I am doing some test on some heads right now. soon as I can get a sbc 1.5 valve I am going to do some flow test with it and see if it is worth doing.

[v6h.o.]

ive been playing with numbers on my Dyno 2003 program for a while now for valve sizes...

i have two sizes picked out for the valves, but they are not as big as Brad proposed. slightly larger than the 3400 setup.

while playing wiht numbers on the program for different engine setups ive tryed larger like what brad suggested but it reduced power most of the time.

[RacerX11]

Does the dyno 2003 program account for the splayed valves? If it is assuming non-splayed valves, and the valve sizes are too big compared to the cylinder bore, the program may take into account the increased shrouding since the valve will be closer to the cylinder wall.

This is important for flow bench testing as well. We need to get flow numbers with both a 3100 and 3400 cylinder bore. I had a chance to get my heads flowbenched when I had them in the shop, but they didn't have the right bore cylinders for the machine, so I passed.

Marty

[AaronGTR]

I just finished porting my 3400 heads. I think the exhaust ports are definitly the most restrictive part and would benefit the most from a larger valve. However, as The Raven pointed out, the valve seats are VERY close together, not leaving much room for anything bigger. I don't think you could fit a bigger intake valve in. You could maybe fit a bigger exhaust valve, but you'd have to have the seat inlarged offset away from the intake port. Not worth it IMO. Better off just waiting for a cam with more lift and duration to move the gasses than trying for bigger valves. That and doing the best P&P you can do of course. FYI, the heads I got were already ported by RSM racing, and I was not happy at all with the job they did. Unfortunate since I like everything else I've got from them. They missed quite a lot of casting around the valve guides, and left the exhaust ports pretty rough. I cleaned up the intakes a little but left them slightly rough, and really smoothed out the exhaust ports. Should flow well now.

[1QUICKHATCH]

I just finished porting my 3400 heads. I think the exhaust ports are definitly the most restrictive part and would benefit the most from a larger valve. However, as The Raven pointed out, the valve seats are VERY close together, not leaving much room for anything bigger. I don't think you could fit a bigger intake valve in. You could maybe fit a bigger exhaust valve, but you'd have to have the seat inlarged offset away from the intake port. Not worth it IMO. Better off just waiting for a cam with more lift and duration to move the gasses than trying for bigger valves. That and doing the best P&P you can do of course. FYI, the heads I got were already ported by RSM racing, and I was not happy at all with the job they did. Unfortunate since I like everything else I've got from them. They missed quite a lot of casting around the valve guides, and left the exhaust ports pretty rough. I cleaned up the intakes a little but left them slightly rough, and really smoothed out the exhaust ports. Should flow well now.

you have any pic's of your heads and did they give you flow #s when you bought them?

[v6h.o.]

marty i know my program alows for a head setup with "canted valves" but i think when i do custom head flow numbers this option doesnt apply... i cant remember exacly, its been a month or two since ive played with the engines on there.

i'll have to take a look when i get settled back in here (just moved)

you may be right on that.

i think i was using a 1.78(or was it 1.75?) inch intake valve and 1.445 exh valve in the dyno program. which seemed to pull good numbers.


i cant believe you bought RSM's head Aaron.. they over charge and the quality is just shit. the $ they charge for ported heads is rediculous. ive seen 2 rsm ported heads.. wasnt impressed.

[smilinguy99]

Happened upon this link:

http://popularmechanics.com/automotive/sub_concept_gmtoys/2001/1/Malibu_Sport/print.phtml

It is a Malibu concept car from a few years ago. The thing has a 3.4 out of a Venture with 1.80" valves. Factory might know something about what works , I dunno. Or maybe they just put big valves in it because they could.

sg99

[AaronGTR]

1QUICKHATCH... I'll be posting pics in a week or two when I get everything re-assembled and installed on the car. No, they didn't give me any flow #'s. I wish they did.

v6h.o. ... yeah, I agree their porting wasn't very good at all. Wish I had known that at the time, but like I said, everything else I've bought from them was nice. The only reason I did buy them was because I couldn't have my car down while I took my own heads off for porting locally, and RSM was actually the cheapest place I found were you can order ported heads. I guess I would've been better off getting a set from a wrecked car and having them done. Live and learn.

[AaronGTR]

BTW, anyone know what is up with the title under my name? How do I change it? I don't know if it's supposed to be some kind of sick joke or something, but it's far from humorus.

[v6h.o.]

v6h.o. ... and RSM was actually the cheapest place I found were you can order ported heads. I guess I would've been better off getting a set from a wrecked car and having them done. Live and learn.

hmm guess you didnt shop around. i charge $ 750 Canadian for a set of P&P heads, with 3 angle valve job, resurfaced to customer spec, bead blasted and cleaned, and heads are checked for cracks before any work is done.

[AaronGTR]

How would I know you offer heads? I've never heard of you before I came to this site. Try advertising over at grandamgt.com, because that's where I get most of my info, and at the time I bought the heads (last summer), there were only three places I found.


BTW people, still waiting for an answer to the question in my last post.

[RacerX11]

The titles under people's names change based on your post count. Get more posts, and you will get a new one. It is the same for everybody. Nobody is picking on you, so don't get your panties in a bunch.

Marty